Device and method for feeding fuel

ABSTRACT

The present invention provides a fuel feeding apparatus and method for improving the controllability of mixing process and mixing ratio of fuel and combustion air, and a combustion system and method for effecting new combustion properties. The fuel feeding apparatus of the combustion system has fuel feeding means, combustion gas extraction means, steam supply means, mixing means and fuel gas introduction means. The combustion gas extraction means extracts combustion gas of a combustion area therefrom. The mixing means mixes the fuel of fuel feeding means with at least one of combustion gas extracted from the furnace and steam of a steam generator. The fuel gas introduction means introduces a mixed fluid of combustion gas, steam and fuel to the combustion area as a fuel gas, and allows the fuel gas to be mixed with the combustion air. A step of mixing the fuel with the combustion gas after extracted from the furnace and a step of mixing the fuel gas with the combustion air are stepwisely carried out, so that the controllability of mixing process and ratio of the air and fuel is improved. Such a control of fuel gas flow enables control of characteristics of flame and production of flame with new properties in the combustion area.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to apparatus and method for feeding fuel,and more particularly, to such apparatus and method for improvingcontrollability of mixing of fuel and combustion air, characteristics ofcombustion of fuel, and further, properties of flame in a combustionarea, and so forth.

BACKGROUND OF THE INVENTION

An industrial furnace, such as a tubular furnace, metal heating furnace,ceramic industrial kiln, metal melting furnace, gasification meltingfurnace, boiler or a combustion heating type of heating apparatus, suchas a radiant tube burner, is provided with fuel feeding means forfeeding hydrocarbonaceous fuel, air supply means for supplyingcombustion air, and a combustion means for mixing the fuel andcombustion air to burn the fuel, such as a burner. The fuel andcombustion air mixed in the combustion means produce flame in acombustion area by diffusion combustion. In this kind of combustionmeans, the actual amount of combustion air is set to be an excess airratio exceeding a theoretical amount of air for the fuel, and the mixingratio of combustion air and fuel (air-fuel ratio) is, in general, set tobe approximately 14.15. Generally, pre-mixing of fuel and combustion airbefore fed to a burner is not adopted, because of its possibility ofunexpected back fire, and therefore, the combustion air and fuel areintroduced into a burner throat or in-furnace area through an airdelivery port and fuel injection port so as to be mainly mixed in aproximal zone of the burner. For instance, a burner is provided with aflame stabilizer of swirler type, flame holder type or the like, inorder to desirably mix a fuel injection flow and an air flow havingdifferent flow rates. The flame stabilizer causes an ignitablehigh-temperature circulation flow in the mixing area of fuel and air,whereby it prevents blow-off of flame and ensures stability of flame.

On the other hand, combustion gas produced in a furnace circulates inthe in-furnace area. The combustion gas in the furnace is exhaustedtherefrom as the combustion air and fuel enter into the furnace. Thecombustion gas still possesses a large amount of recoverable heat, andtherefore, the combustion gas is exhausted to the ambient environmentthrough a waste-heat recovery equipment, such as a heat exchanger,waste-heat boiler and the like. In general, such an equipment preheatscombustion air or heats a fluid useful as a heat medium.

A part of in-furnace combustion gas forms an in-furnace re-circulationflow to be mixed with the combustion air and/or fuel injection flow, sothat ignition of fuel is urged and a slow combustion reaction of a lowoxygen density is promoted. Recently, mixing of combustion gascirculation flow with combustion air or fuel is considered to beimportant, since such mixing is effective to prevent a local heat offlame and restrict production of nitrogen oxide (NOx).

Mixing process and ratio of fuel injection flow, combustion air flow andcombustion gas re-circulation flow are changed, depending on positions,structures and configurations of combustion air port and fuel injectionport, and an arrangement and structure of combustion furnace, and soforth. Further, mixing control for various kinds of fluid in a furnaceis closely associated with unexpected control parameters, such as changeof furnace temperature, heat load, in-furnace circulation flow and soforth. Therefore, it is difficult to readily control the mixing processand ratio. Especially, as regards a combustion furnace which relativelyoften varies in heat load and furnace temperature in correspondence withits operating condition, mixing of combustion gas re-circulation flowwith air and/or fuel might result in deterioration of combustionstability when the temperature of combustion air is lowered, andtherefore, any countermeasure for overcoming this drawback is required.Thus, development of fuel feeding device is desired which enablesoptional and variable control of the mixing process and mixing ratio offuel, combustion air and combustion gas, and which can normally optimizea combustion reaction in a combustion area.

Further, an extremely high-temperature air combustion method developedby the present applicant is known in the art, wherein combustion air ispreheated up to a temperature equal to or higher than 800 degreescentigrade (deg. C.) and introduced into a mixing area or combustionarea. A combustion mode of flame by the preheated air at a temperatureequal to or higher than 800 deg. C. provides combustion stability in acombustion atmosphere with a wide range of air ratio, compared to acombustion mode of normal flame by air preheated to a temperature lowerthan 400 deg. C., or a combustion mode of transitional flame at atemperature of 400.800 deg. C. The combustion stability in the extremelyhigh-temperature air combustion method is considered to result from itscombustion characteristics entirely different from the conventionalmethod, owing to increase of reaction rate by a higher temperature ofpreheated air. Especially, when the combustion air or mixed gas forcombustion is heated to a temperature higher than the self-ignitiontemperature of fuel, a combustion reaction without necessity of externalignition means can be realized in an ignition process. Further, flamefailure can be prevented in spite of substantial increase of combustionair flow speed, so that the combustion air can be fed to a combustionarea or mixing area as a high speed air flow. Furthermore, althoughincrease of flame volume and decrease of flame brightness in accordancewith the extremely high-temperature air combustion method are observedin the combustion area, phenomenon of local heat generation isrestricted, so that a temperature field in the combustion area isrendered uniform.

Conventional research of radiation and convection heat transfer effectswith respect to heating apparatus such as a tubular furnace is mainlydirected to development of a combustion system which can generate adesirable temperature field in a combustion area while preventing alocal overheat of a heated tube, or improvement of an arrangement andstructure of the tubes and so forth. However, mixing of air and fuelgenerally tends to depend on control of temperature, flow rate, flowvelocity, direction of air flow and the like, and therefore,characteristics of flame in a combustion area substantially rely onproperties and fluid characteristics of air flow. For example, sincefuel and air taking a combustion reaction in a mixing area almostentirely burn near a burner, a flame is merely formed near the burner,and therefore, it is difficult for the flame to reach a zone near aheated subject. On the other hand, if a feeding pressure of fuel isincreased or a diameter of fuel nozzle is reduced for increasing adistance of travel of fuel fluid, a blowing speed of the fuel may beincreased. However, the flow rate of fuel fluid is greatly smaller thanthat of air flow, and therefore, owing to a power of a large amount ofair, the power of fuel fluid flow is de-energized to lose its powerimmediately after its injection. Thus, it is difficult to increase adistance of travel of the fuel fluid.

On the contrary, according to the extremely high-temperature aircombustion method as set forth above, an air ratio and air-fuel ratiocan be reduced and a flow rate of circulation flow of in-furnacecombustion gas can be increased, whereby a slow combustion reaction canbe maintained in a furnace and a temperature field in the furnace can berendered in a uniform condition. However, in this kind of combustionmethod, a supply velocity of air flow tends to be set in a relativelyhigh value. Therefore, the tendency that the control of mixing of fueland air depends on control of air flow is more significantly revealed.

In addition, it has been found, in the extremely high-temperature aircombustion method, that a mixing condition of a fuel injection flow,combustion air flow and in-furnace circulation flow is an importantfactor for controlling a combustion reaction, and therefore, it isnecessary to focus on the mixing control of these three kinds of fluidsupon adoption of an arrangement of apparatus. However, it is difficultin practice to surely control the mixing of these fluids in dependenceon a conventional combustion skill in which an in-furnace circulationflow of combustion gas is mixed with a fuel or air flow within anin-furnace area of the furnace. Thus, development of a new combustionskill is desired, in which controllability of fuel flow itself deliveredinto a furnace is improved, and a position, diffusing manner and reachof flame can be controlled in dependence on control of the fuel flow,and further, controllability of mixing position and mixing ratio offuel, combustion air and combustion gas can be improved.

It is therefore an object of the present invention to provide a fuelfeeding apparatus and method which can improve controllability of mixingprocess and mixing ratio of fuel and combustion air.

Another object of the present invention is to provide a fuel feedingapparatus and method which allow a fuel and combustion gas to beoptionally mixed, independently of control of in-furnace combustion gasre-circulation flow.

Still another object of the present invention is to provide a fuelfeeding apparatus and method which can produce a fuel gas having newcombustion characteristics.

Another object of the present invention is to provide a combustionsystem and method which can improve controllability of fuel flowentering a combustion s area and which enable control of characteristicsof flame by control of fuel flow, and further, a heating apparatus andmethod which can control properties of flame acting on heated subjects.

DISCLOSURE OF THE INVENTION

To attain these objects, the present inventors found in a research thathigh temperature combustion gas extracted from a furnace is mixed with afuel, or steam is added to the combustion gas for adjusting the contentof steam in the combustion gas and the gas is then mixed with the fuel,or otherwise, high temperature steam is mixed with a fuel, wherebymixing of fuel and combustion gas can be surely controlled and a largequantity of fuel gas presenting new combustion characteristics can beproduced. The present inventors achieved the present invention asdescribed hereinbelow, based on such recognition.

The present invention provides an apparatus for feeding fuel which hasfuel feeding means for feeding the fuel and combustion air supply meansfor supplying combustion air to a combustion area, said apparatuscomprising:

mixing means for mixing the fuel of said fuel feeding means withcombustion gas extracted from a furnace and/or steam of steam supplymeans; and

fuel gas introduction means for introducing a mixed fluid of said fueland said combustion gas and/or steam into said combustion area as a fuelgas so as to mix the fuel gas with said combustion air.

The present invention also provides a method for feeding fuel in whichthe fuel and combustion air is fed to a combustion area, said methodcomprising:

feeding combustion gas extracted from a furnace and/or steam of steamsupply means to a mixing area;

feeding said fuel to said mixing area to produce a mixed fluid of thefuel and said combustion gas and/or steam; and

introducing said mixed fluid into said combustion area as a fuel gas soas to mix the fuel gas with the combustion air, thereby causing acombustion reaction of said fuel gas in said combustion area.

According to the arrangement of the present invention, the fuel is mixedwith either or both of combustion gas extracted from a furnace and steamof steam supply means. The step of mixing the fuel with the combustiongas and/or steam, and the step of mixing the mixed fluid with combustionair are stepwisely carried out, and therefore, flexibility andreliability of mixing control of fuel, combustion air and combustion gasand/or steam are significantly improved. A large quantity of mixed fluidcontaining a thin fuel component is produced in the mixing area of thefuel and combustion gas and/or steam. The mixed fluid is fed to thecombustion area, as being a large quantity of fuel gas flow having amomentum controllable independently of in-furnace combustion gascirculation flow. Accordingly, the fuel gas flow introduced into thefurnace can mix with the combustion air flow without being substantiallysubject to influence of in-furnace combustion gas circulation flow.Thus, mixing process and mixing ratio of fuel and combustion gas can bevariably controlled, independently of control of in-furnace combustiongas re-circulation flow.

From another aspect of the present invention, this invention provides acombustion system comprising the apparatus for feeding fuel as set forthabove, and combustion air supply means for feeding the combustion air tothe combustion area. The present invention further provides a combustionmethod including the method for feeding fuel as set forth above, whereinsaid mixed fluid is introduced into the combustion area as the fuel gas,and the fuel gas is mixed with the combustion air to cause a combustionreaction of the fuel gas in the combustion area.

According to such an arrangement, a large quantity of fuel gas flow withan independently controllable momentum is introduced into the combustionarea, so that the characteristics of flame produced in the combustionarea can be controlled by control of fuel gas flow introduced into thecombustion area as well as control of combustion air flow. Further, thefuel is preliminarily mixed with the combustion gas and/or steam, andthereafter, mixed with the combustion air, so that flexibility andreliability of mixing control of fuel and combustion air issignificantly improved, in comparison with a conventional combustionmethod in which air and/or fuel is mixed with in-furnace circulationflow in the furnace.

From still another aspect of the present invention, this inventionprovides a heating apparatus comprising the combustion system of theaforesaid arrangement, and a heating method wherein a subject to beheated is heated by flame produced by the combustion method of aforesaidarrangement.

According to this invention, characteristics of flame produced in thecombustion area can be controlled by controlling a relatively largequantity of fuel gas containing a thin fuel, whereby an exothermiccombustion reaction in the combustion area can be adjusted, andradiation and convection heat transfer effects of flame acting on theheated subject can be improved.

In the present specification, the term reading “fuel gas” means a mixedgaseous fluid which comprises a fuel mixed with combustion gas and/orsteam and which contains a fuel component having a combustion reactivitywith combustion air. The fuel component in the fuel gas is activated bymixing with high-temperature combustion gas and/or steam, whereas thecombustion gas of a low oxygen density restricts the combustion reactionof the fuel component. Such a fuel gas is introduced into the combustionarea as being a high-temperature fuel gas of a low oxygen densitycontaining an activated and thin fuel component, and presents newcombustion characteristics different from those of a conventional fuel.For instance, the fuel gas introduced into the combustion area slowlytakes a combustion reaction with the combustion air, without mixing withthe in-furnace combustion gas, whereby a relatively low-temperaturediffusion flame in a wide area, which restricts a local heat andproduction of nitrogen oxides (NOx), is produced in the furnace.

If desired, a part of combustion gas and/or steam may be mixed withcombustion air. The combustion air, which is diluted with the combustiongas and/or steam to have a low oxygen density, is introduced into thecombustion area to be mixed with the high-temperature fuel gas of a lowoxygen density as set forth above. The fuel component contained in thefuel gas more slowly takes a combustion reaction with the combustion airof a low oxygen density so as to produce a low-temperature flame in awide area with a local heat of flame being restricted.

Further, steam contained in the combustion gas, high-temperature steamheated by mixing or heat exchange with the high-temperature combustiongas, or high temperature steam heated up to a temperature equal to orhigher than 700 deg. C. by independent steam heating means, causes athermal decomposing reaction and/or a steam reforming reaction of fuelhydrocarbon, and therefore, the fuel hydrocarbon is reformed to a highquality reformed gas containing a relatively large quantity ofhydrocarbon radical, hydrogen, carbon, carbon monoxide and so forth.Thus, it is possible to reform a relatively heavy gravity or low (ordegraded) quality hydrocabonaceous fuel, such as heavy oil, to a lightgravity or high (or good) quality hydrocabonaceous fuel, before the fuelis mixed with the combustion air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are block flow diagrams of fuel feeding apparatusillustrating preferred embodiments of the present invention.

FIG. 5 is a schematic cross-sectional view of a combustion systemprovided with the fuel feeding apparatus as shown in FIGS. 1(A) and1(B).

FIG. 6 is a schematic vertical cross-sectional view showing anotherarrangement of combustion system provided with the fuel feedingapparatus as shown in FIG. 1(B).

FIG. 7 is a block flow diagram schematically illustrating actions of thefuel mixing device as shown in FIG. 6.

FIG. 8 is a schematic vertical cross-sectional view of a combustionsystem provided with the fuel feeding apparatus as shown in FIG. 1(C).

FIG. 9 is a schematic vertical cross-sectional view of a combustionsystem provided with the fuel feeding apparatus as shown in FIGS. 2(A)and 2(B).

FIG. 10 is a schematic vertical cross-sectional view of a combustionsystem provided with the fuel feeding apparatus as shown in FIG. 2(B).

FIG. 11 is a schematic vertical cross-sectional view of a combustionsystem provided with the fuel feeding apparatus as shown in FIG. 3(A).

FIG. 12 is a schematic vertical cross-sectional view of a combustionsystem provided with the fuel feeding apparatus as shown in FIG. 3(B).

FIG. 13 is a schematic vertical cross-sectional view of a combustionsystem provided with the fuel feeding apparatus as shown in FIG. 3(C).

FIG. 14 is a schematic vertical cross-sectional view of a combustionsystem provided with the fuel feeding apparatus as shown in FIG. 4.

FIGS. 15 and 16 are cross-sectional views of a steam heating device asshown in FIG. 14.

FIGS. 17 to 22 are cross-sectional views illustrating first throughsixth examples of the fuel feeding apparatus and combustion systemaccording to the present invention.

FIG. 23 is a schematic plan view of an example of heating device inaccordance with the present invention.

FIGS. 24 and 25 are schematic plan views illustrating alternativeexamples of the heating device, FIG. 24 showing an operation mode of theheating device in a cold period and FIG. 25 showing an operation modethereof in a hot period.

FIG. 26 is a schematic vertical cross-sectional view showing acontinuous firing type of heating furnace according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

A fuel feeding device as shown in FIG. 1(A) comprises a combustion gasextraction passage for extracting a combustion gas from a combustionarea, a mixing area for a fuel and the combustion gas, and a fuel supplypassage for feeding the fuel to the mixing area. The high-temperaturecombustion gas produced in the combustion area is extracted therefromthrough the combustion gas extraction passage. A predetermined flow rateof combustion gas is exhausted out of the system as a combustion exhaustgas, and the reminder thereof is introduced into the mixing area. Ifdesired, steam of a steam generator is injected into the combustion gasso as to adjust the content of steam in the combustion gas. Ahydrocarbonaceous fuel is introduced into the mixing area through thefuel supply passage to be mixed with the combustion gas, so that a hightemperature mixed gas (a fuel gas) comprising the fuel diluted with thecombustion gas is produced in the mixing area.

In general, the combustion gas merely has a residual oxygen density in arange of 0%.10%, so that the fuel in the fuel supply passage is mixedwith the combustion gas without substantially taking a combustionreaction with the combustion gas. The temperature of combustion gas issubstantially equal to the temperature of combustion area, andtherefore, the mixed gas containing a small quantity of low-temperaturefuel still keeps a temperature slightly lower than the temperature ofcombustion gas, e.g., a temperature in a range of 800 deg. C. 1200 deg.C. In such a high-temperature mixed gas, the steam contained in thecombustion gas reforms the fuel to activate the fuel. As a result, thefuel is apt to take a combustion reaction, compared to a fuel at anormal temperature. On the other hand, the combustion gas of a lowoxygen density restricts the combustion reaction of the fuel.

The flow rate of combustion gas is extremely large in comparison withthe flow rate of fuel feed, and therefore, the mixed gas is introducedinto the combustion area as a large quantity of fuel gas containing athin fuel. Combustion air is introduced into the combustion area througha combustion air supply passage, and the flow of mixed gas is mixed withthe flow of combustion air in the combustion area to take a combustionreaction without being substantially subject to an influence ofcirculation flow of combustion gas.

A gaseous, liquid, solid or semi-solid fuel may be employed as the fuel.For instance, in a case where a hydrocabonaceous gaseous fuel such asmethane is used as the above fuel, the gaseous fuel flows into thecombustion area as being the high-temperature fuel gas diluted by thecombustion gas. It is possible to produce a high quality reformed gascontaining a relatively large quantity of hydrocarbon radical, hydrogen,carbon, carbon monoxide and the like by means of a thermal decompositionreaction and/or a steam reforming reaction of the fuel, which can becaused during the mixing and introduction processes of the fuel andcombustion gas, and the reformed gas can be fed to the combustion areaas being the fuel gas. Further, in a case where a hydrocabonaceousliquid fuel is used as the aforementioned fuel, a reforming reaction ofthe fuel including a vaporization and thermal decomposition processesoccurs in the mixing area and introduction passage so that a highquality fuel gas (reformed gas) can be fed to the combustion area.Furthermore, in a case where a solid fuel, such as pulverized coal, isused as the fuel, the fuel is suspended in the high-temperaturecombustion gas and thermally decomposed in the mixing area andintroduction passage, so that a high quality fuel gas containinghydrocarbon radical, hydrogen, carbon and carbon monoxide can be fed tothe combustion area. It is considered that steam contained in thecombustion gas substantially affects such a reforming action of thehydrocabonaceous fuel. Therefore, if desired, the aforementioned steamgenerator adds a quantity of steam to the combustion gas to increase thecontent of steam in the combustion gas, thereby promoting the steamreforming reaction of the fuel.

A schematic cross-sectional view of the combustion system provided withthe fuel feeding apparatus as shown in FIG. 1(A) is illustrated in FIG.5(A). The combustion apparatus is provided with a combustion chamber 1,a forced draft fan 2 and a combustion air supply device 30, and further,it includes a fuel mixing device 10 and an exhaust gas circulation fan 3which constitute the fuel feeding apparatus. The fan 2 sucks a quantityof atmospheric air through an air intake passage OA and presses it intoa combustion air supply passage CA. The combustion air supply device 30has a combustion air outlet port 35 opening in the combustion chamber 1,and the combustion air in the passage CA flows into the chamber 1through the outlet port 35. The fan 3 induces the combustion gas in thechamber 1 through a combustion gas extraction port 90 and combustion gasextraction passages EX, ER, and feeds the combustion gas to the fuelmixing device 10 through a combustion gas introduction passage RG. Asteam generator 8 such as a steam boiler is connected with the passageRG by means of a steam supply passage ST, a quantity of superheatedsteam at a temperature of 150 deg. C.300 deg. C. is injected into thegas to adjust the content of steam in the combustion gas. A part ofcombustion gas is exhausted out of the system through an exhaust gaspassage EG.

The fuel mixing device 10 positioned inside of the combustion air supplydevice 30 has a fuel nozzle 11, a combustion gas introduction part 12, amixing area 15 and a fuel injection port 16. The nozzle 11 is adapted toinject the feed fuel feed of a fuel supply passage F to the mixing area15, the introduction part 12 introduces the combustion gas (and steam)of the passage RG into the mixing area 15. The mixing area 15 allows thefuel to be mixed with the combustion gas (and steam), and injects themixed gas (fuel gas) into the combustion chamber 1. The flow rate,injection pressure and direction of the mixed gas to be injected intothe chamber 1 are controlled by the flow rate, injection pressure anddirection of the fuel and combustion gas injected by the nozzle 11 andintroduction part 12, and they are restricted by the structure of themixing area 15.

The mixed gas injected into the chamber 1 is mixed with the combustionair delivered from the combustion air supply device 30 to take acombustion reaction. The mixed gas at a flow rate roughly equal to aflow rate of the combustion air has a momentum corresponding to that ofthe combustion air flow, so that the mixed gas flows in a direction setby the fuel mixing device 10 and mixes with the combustion air, withoutbeing subject to a substantial influence of buoyancy due to atemperature variation, and direction and force of the combustion airflow. The combustion reaction of mixed gas is restricted by thecombustion gas at a low oxygen density, and the mixed gas slowly takes acombustion reaction with the combustion air. Therefore, the mixed gasdiffusing in the combustion area ensures its intended distance oftravel, so that a flame is desirably produced in the predeterminedin-furnace region without flame being locally and aggregately producedonly in vicinity of the devices 10, 30.

According to such a fuel feeding method, a step of mixing the fuel withthe combustion gas after extracted from a furnace and a step of furthermixing the mixed fluid of fuel and combustion gas with the combustionair are stepwisely carried out. The composition and flow rate of mixedgas are variably controlled by the flow rate of combustion gas (andsteam) to be introduced into the mixing area 15, the fuel feed rate offuel supply passage F, and the mixing ratio of combustion gas and fuel.The mixing ratio is preferably set in a range between 1:1.20:1. Sincethe high-temperature mixed gas produced in the mixing area is fed to thecombustion area as being a fuel gas having a flow rate considerablygreater than that of fuel itself, the mixed gas mixes with thecombustion air without being mixed with and de-energized by thein-furnace circulation flow of the combustion gas. Therefore, the mixingratio, mixing position, mixing mode and combustion characteristics offuel gas and combustion air can be controlled by adjusting both of thecombustion air flow and fuel gas flow. The mixing ratio of the fuel gasand combustion air is preferably set in a range between 1:10.20:10.Further, the flow velocity of fuel gas entering the combustion area ispreferably set in a range of 10.150 m/s. Thus, the flexibility andreliability of mixing control of the fuel, combustion air and combustiongas are considerably improved, since the mixing process and mixing ratioof fuel and combustion gas can be optionally controlled, without beingsubstantially subject to the influence of recirculation flow ofin-furnace combustion gas. In addition, a zone of combustion reaction,and a position and orientation of flame and the like can be controlledby control of the flow velocity, flow rate and direction of the mixedgas (fuel gas) which has been increased in volume by addition of thecombustion gas (and steam).

Further, the aforementioned mixed gas is introduced into the combustionarea as being a high-temperature fuel gas at a low oxygen density whichcontains activated and diluted fuel components, so as to take a slowcombustion reaction with the combustion air. As a result, a diffusioncombustion of relatively low-temperature flame in a wide area isgenerated within the furnace, which flame is advantageous in restrictionof local exothermic heat and reduction of nitrogen oxides (NOx)production. In addition, the mixing ratio of fuel and combustion air canbe variably controlled by the above fuel feeding device, in response tovariation of the in-furnace temperature and heat load. This ispractically advantageous in a heating furnace and the like in which thein-furnace temperature and heat load fluctuate.

Another embodiment of the present invention is shown in FIG. 1(B). Inthe fuel feeding device as shown in FIG. 1(B), the circuit including theextraction passage, mixing area and introduction passage is providedwith circulation means for forcibly circulating a gaseous fluid, such asa forced circulation fan, and a heat exchanger for transitionallycooling the combustion gas in order to reduce the heat load and thermalstress of the circulation means. The heat exchanger comprises a coolingpart for transitionally cooling the high-temperature combustion gas, anda heating part for re-heating the cooled combustion gas. The combustiongas extracted from the combustion area is cooled by the cooling partdown to a temperature approximately in range of 200 deg. C.300 deg. C.,and the sensible heat gained in the cooling part is emitted to thecooled combustion gas by the heating part. The combustion gas cooled inthe cooling part is, if desired, mixed with steam and thereafter, heatedin the heating part up to a temperature equivalent to its temperatureimmediately after extraction. The combustion air is supplied to thecombustion area through an air pre-heater which pre-heats the air to anextremely high-temperature range equal to or higher than 800 deg. C.,preferably equal to or higher than 1000 deg. C.

FIG. 5(B) is a schematic cross-sectional view of the combustion systemprovided with the fuel feeding apparatus as shown in FIG. 1(B). Thecombustion system is provided with a combustion chamber 1, a forcedcirculation fan 2, an exhaust gas circulation fan 3, a steam generator8, a fuel mixing device 10 and an air supply device 30 which aresubstantially the same as those shown in FIG. 5(A). The combustionsystem further comprises heat exchangers 13, 33 and a forced exhaust fan4, and the heat exchangers 13, 33 have regenerators 14, 34 divided intoa plurality of sections, respectively. The heat exchanger 13 constitutesa cooling part and heating part as shown in FIG. 1(B), and the heatexchanger 33 constitutes an air pre-heater as shown in FIG. 1(B). Ahigh-cycle switching type of regenerative heat exchanger with a rotarydisc type of passage change-over means 20,40 is preferably used as theheat exchanger 13,33 and a ceramic regenerator of a honey-comb structureprovided with a large number of narrow fluid passages is preferablyemployed as the regenerator 13, 14. The construction of this kind ofregenerator is disclosed in detail, e.g., in Japanese patent applicationNo. 7-284825 (Japanese patent laid-open publication No. 9-126675) of thepresent applicant and therefore, a further detailed explanation thereonis omitted.

The fan 2 connected with an atmospheric air intake passage OA and an airsupply passage CA introduces the combustion air into the heat exchanger33. The fan 4 induces the combustion gas of the combustion chamber 1through an exhaust passage E1, heat exchanger 33 and exhaust passage E2.The respective sections of regenerator 34 are alternately inheat-transfer contact with a high-temperature combustion exhaust gas anda low-temperature combustion air so that the sensible heat of combustionexhaust gas is transmitted to the combustion air to heat the air up to ahigh-temperature range equal to or higher than 800 deg. C. Thehigh-temperature combustion air is fed to the air supply device 30through a high-temperature air supply passage SA and the air flows intothe combustion chamber 1 through an outlet port 35. The combustionexhaust gas of the exhaust passage E2 cooled down to a temperature rangeof approximately 200 deg. C.300 deg. C. is exhausted out of the systemthrough an exhaust passage E3.

The fan 3 connected with exhaust gas circulation passages R3, R4 inducesthe combustion gas of the combustion chamber 1 through a combustion gasextraction port 90, a combustion gas extraction passage EX and the heatexchanger 13. The section of the regenerator 14 at a low-temperature isin heat-transfer contact with the combustion gas at a high-temperatureso that it accumulates the heat and cools the combustion gas. The cooledcombustion gas is pressed by the fan 3 and if desired, is mixed withsteam of the steam generator 8 and thereafter, is in heat-transfercontact with the high-temperature section of the regenerator 14 whichhas been heated with the heat accumulation. The combustion gas (andsteam) cools the regenerator 14 and gains the heat therefrom to beheated up to the extremely high temperature range equal to or higherthan 800 deg. C., preferably, equal to or higher than 1000 deg. C. Thecombustion gas is fed to the fuel mixing device 10 through a combustiongas introduction passage RG as being the high-temperature combustiongas. If desired, a part of the combustion gas is exhausted through anexhaust gas passage EG as a combustion exhaust gas.

According to the embodiments as shown in FIGS. 1(B) and 5(B), the fuelfeeding device is provided with the circulation passage of thecombustion gas EX, RG in which the heat exchanger 13 constituting thecooling part and heating part is interposed, and therefore, the heatload and thermal stress on the fan 3 are greatly relieved. Further, thefuel feeding device is in association with the heat exchanger 33 forpre-heating the combustion air to the aforementioned extremelyhigh-temperature range so that the combustion area of the combustionchamber 1 is supplied with an extremely high-temperature pre-heated air.

In general, it is found that the combustion reaction by such anextremely high-temperature pre-heated air can be successfully performedin the existence of high speed flow of combustion air, and the velocityof the air flow can be set to be equal to or higher than 10 m/s. Thehigh speed air flow activates the re-circulation of in-furnacecombustion gas, and also forms an extensive combustion reaction zone inthe combustion chamber 1. In addition, the mixed gas containing a largequantity of combustion gas of low oxygen density effects a self ignitionwhen mixing with the combustion air pre-heated to the extremely hightemperature, thereby generating a high-temperature combustion atmosphereof low oxygen density in the furnace. The fuel components contained inthe mixed gas are subject to the effects of promotion of combustionreaction by the high-temperature combustion atmosphere, activation offuel by pre-mixing with the combustion gas (and steam), restriction ofcombustion reaction involved in the low oxygen density, and extension ofcombustion reaction zone owing to the high speed flow, and the like, sothat the fuel takes a slow combustion reaction in a wide area to createa relatively low temperature and extensive flame in the combustion area.Such a high-temperature combustion atmosphere of a low oxygen density iseffective in restriction of local exothermic heat and reduction ofnitrogen oxides (NOx) production.

FIG. 6 is a schematic cross-sectional view of another combustion systemprovided with the fuel feeding device as shown in FIG. 1(B). FIG. 6(A)shows a first combustion step of the combustion system and FIG. 6(B)shows a second combustion step thereof. In FIG. 6, constituents, whichare substantially the same as those of the aforementioned embodiments orequivalent thereto, are indicated by the same reference numerals.

The combustion system as shown in FIG. 6 is provided with a pair of fuelmixing devices 10A, 10B and a pair of air supply devices 30A, 30B. Thecombustion system differs from that shown in FIG. 5(B) in theconstruction of heat exchanger, wherein the fuel mixing device 10A, 10Bcontains a regenerator 14 and the air supply device 30A, 30B contains aregenerator 34, respectively. A ceramic regenerator with a honey-combstructure is preferably employed as the regenerator 14, 34. Thecombustion system is also provided with fluid passage change-over means20 for switching the passage of combustion gas and fluid passagechange-over means 40 for switching the passage of combustion air. Thechange-over means 20, 40 is alternately switched to either of the firstposition (FIG. 6A) and the second position (FIG. 6B) in a predeterminedtime interval, which is set to be no longer than 60 seconds.

In the first combustion step (FIG. 6A), an air draft fan 2 introducesthe atmospheric air of an air intake passage OA into the change-overmeans 40 so that the combustion air is fed to the air supply device 30Athrough the passage L1. The combustion air is in heat-transfer contactwith the regenerator 34 of the air supply device 30A to be heated up tothe extremely high-temperature range as set forth above by the heatemission of the regenerator 34, and thereafter, the air flows into thecombustion chamber 1 through an air outlet port 35. An exhaust fan 4exhausts the combustion gas of the chamber 1 from the system through theair supply device 30B, a passage L2, the change-over means 40 andexhaust passages E2, E3. The regenerator 34 of the device 30B is heatedin heat-transfer contact with the high-temperature combustion gas, andthe combustion gas is cooled down.

An exhaust gas circulation fan 3 induces the combustion gas of thecombustion chamber 1 through the fuel mixing device 10B, exhaust gascirculation passages R2, R3 and the change-over means 20, and feeds thecombustion gas to the fuel mixing device 10A through the change-overmeans 20 and exhaust gas circulation passages R4, R1. Thehigh-temperature combustion gas of the chamber 1 through the device 10Bis cooled down in heat-transfer contact with the regenerator 14 of thedevice 10B, and the gas heats the regenerator 14. The cooled combustiongas is, if desired, mixed with a quantity of steam of a steam generator8, and is fed to the device 10A under the circulation pressure of thefan 3 to flow through the regenerator 14 of the device 10A so as to beheated up to the extremely high-temperature range as set forth above byheat exchange with the high-temperature regenerator 14. A fuel nozzle 11of the device 10A delivers the fuel to the heated combustion gas (andsteam), so that the mixed gas of combustion gas and fuel enters into thecombustion chamber 1 through a fuel gas injection port 16 as a fuel gas.

In the second combustion step (FIG. 6B), the combustion air is suppliedto the air supply device 30B through the air intake passage OA, the airsupply passage CA, the change-over means 40 and the passage L2. Thecombustion air is in heat-transfer contact with the regenerator 34 ofthe device 30B to be heated up to the extremely high-temperature rangeas set forth above, and the air flows into the combustion chamber 1through the air outlet port 35 as the high-temperature combustion air.The exhaust fan 4 exhausts the combustion gas from the system throughthe air supply device 30A, the passage L1, the change-over means 40 andthe exhaust passages E2, E3. The regenerator 34 of the device 30A isheated in heat-transfer contact with the high-temperature combustiongas, whereas the combustion gas is cooled down.

The exhaust gas circulation fan 3 induces the combustion gas of thecombustion chamber 1 through the fuel mixing device 10B, the exhaust gascirculation passages R1, R3 and the change-over means 20, and feeds thecombustion gas to the fuel mixing device 10B through the change-overmeans 20 and the exhaust gas circulation passages R4, R2. Thehigh-temperature combustion gas of the chamber 1 is cooled down inheat-transfer contact with the regenerator 14 of the device 10A, and thegas heats the regenerator 14. The cooled combustion gas is, if desired,mixed with a quantity of steam of the steam generator 8, and is fed tothe device 10B under the circulation pressure of the fan 3 to be heatedup to the extremely high-temperature range as set forth above by heatexchange with the regenerator 14 of the device 10B. The fuel nozzle 11of the device 10B delivers the fuel to the heated combustion gas (andsteam), so that the mixed gas of combustion gas and fuel flows into thecombustion chamber 1 through the fuel gas injection port 16 as a fuelgas.

FIG. 7 is a block flow diagram illustrating the action of the devices10A, 10B as shown in FIG. 6. FIG. 7(A) shows the first combustion stepof the combustion system and FIG. 7(B) shows the second combustion stepthereof.

According to the arrangement of the aforementioned combustion system,the combustion gas of the combustion chamber 1 is extracted from thecombustion area through one of the fuel mixing devices 10, andcirculates through the passages R1.R2 under the circulation pressure ofthe fan 3, and if desired, a quantity of steam is added to thecombustion gas. Then, the gas is fed to the other of the fuel mixingdevices 10 to be reheated and mixed with the fuel, and is introducedinto the combustion area as the fuel gas. The sensible heat of thehigh-temperature combustion gas is transitionally accumulated in theregenerator 14 when the gas exits the furnace, and the heat is emittedto the low-temperature combustion gas immediately before its mixing withthe fuel. The first and second steps are repeatedly and alternatelyperformed in a short time interval so that the combustion gas (andsteam) is continuously cooled and reheated.

Similarly, the repeat of first and second steps allows the combustionair to constantly obtain the sensible heat of the combustion gas bymeans of the regenerator 34 (FIG. 6), and the air is continuouslypre-heated up to the extremely high-temperature range. The mixed gas andcombustion air are introduced into the combustion chamber through theadjacent devices 10, 30 respectively, and in the combustion area, arelatively low-temperature flame is created in a wide area, owing to aslow combustion reaction, increase of volume and velocity of fuel gasflow, increase of velocity of the combustion air flow.

Another embodiment according to the present invention is shown in FIG.1(C). The fuel feeding apparatus as shown in FIG. 1(C) is provided witha cooling part and heating part for the combustion gas, and an airpre-heater, analogously to the embodiment shown in FIG. 1(B). In thepresent embodiment, the mixing area 15 is positioned between the heatingpart and a circulation device. According to this embodiment, a fuel ismixed with the combustion gas (and steam) cooled by the cooling part,and the mixed gas of the mixing area is heated in the heating part up tothe extremely high-temperature as set forth above. The heating processof the mixed gas in the heating part causes a thermal decompositionreaction and a steam reforming reaction of the mixed gas, so that themixed gas is reformed to a high quality fuel gas containing a relativelylarge quantity of hydrocarbon radical, hydrogen, carbon, carbon monoxideand the like.

FIG. 8 is a schematic cross-sectional view of combustion system with thefuel feeding device having the arrangement as shown in FIG. 1(C). FIG.8(A) shows a first combustion step of the combustion apparatus and FIG.8(B) shows a second combustion step thereof. In FIG. 8, constituents,which are substantially the same as those of the aforementionedembodiments or equivalent thereto, are indicated by the same referencenumerals.

The combustion system as shown in FIG. 8 is provided with fuel mixingdevices 10A, 10B containing regenerators 14, and air supply devices 30A,30B containing regenerators 34, and fluid passage change-over means 20,40 for switching passages of fuel gas and combustion air. This isanalogous to the combustion apparatus as shown in FIG. 6. However, inthe combustion system shown in FIG. 8, the regenerator 14 is interposedbetween a combustion chamber 1 and a mixing area 15, so that narrowpassages of the regenerator 14 allows the combustion chamber 1 to be inintercommunication with the mixing area 15.

In the first combustion step (FIG. 8A), a relatively low-temperaturecombustion gas (and steam) fed to a combustion gas introduction part 12of the fuel mixing device 10A is mixed with a fuel delivered from anozzle 11 of the device 10A, and the mixed gas of the combustion gas(and steam) and the fuel flows through the regenerator 14 of the device10A, whereby the mixed gas is heated up to the extremelyhigh-temperature range as set forth above by heat exchange with theregenerator 14. The high-temperature fuel gas enters into the combustionchamber 1 through a fuel gas injection port 16.

In the second combustion step (FIG. 8B), the relatively low-temperaturecombustion gas (and steam) fed to the combustion gas introduction part12 of the fuel mixing device 10B is mixed with the fuel delivered fromthe nozzle 11 of the device 10B, and the mixed gas of the combustion gas(and steam) and the fuel flows through the regenerator 14 of the device10B, whereby the mixed gas is heated up to the extremelyhigh-temperature range as set forth above by heat exchange with theregenerator 14, and thereafter, enters into the combustion chamber 1through the fuel gas injection port 16.

The mixed gas is heated while flowing through the regenerator 14 of thedevices 10A, 10B and takes a thermal decomposition reaction to bereformed to a relatively high quality fuel gas. The mixed gas injectedinto the chamber 1 from the devices 10A, 10B is mixed with thehigh-temperature combustion air from an adjacent combustion air outletport 35, so that an extensive flame is produced in the chamber 1 by thecombustion atmosphere of a low oxygen density at a high-temperature.

The other embodiments are shown in FIGS. 2(A), (B) and (C), which showarrangements generally corresponding to those in FIGS. 1(A), (B) and(C). However, in the embodiments in FIG. 2, a part of combustion gas ismixed with the combustion air. In the fuel feeding device as shown inFIG. 2(A), the combustion gas (and steam) extracted from a furnace isintroduced into a mixing area for mixing with the combustion air as wellas introduced into a mixing area for mixing with the fuel. The fuelfeeding device as shown in FIG. 2(B) has a mixing area for mixing thehigh-temperature pre-heated air and combustion gas so that a part of acombustion gas (and steam) reheated in a heating part is mixed with theair pre-heated to an extremely high-temperature range by ahigh-temperature pre-heater. The fuel feeding device as shown in FIG.2(C) has a mixing area for mixing a combustion air and a low-temperaturecombustion gas (and steam) so that a part of the combustion gas (andsteam) cooled down to a temperature range of 200 deg. C.300 deg. C. in acooling part is mixed with the combustion air at a normal temperaturebefore pre-heated to the high temperature.

According to this embodiment, the oxygen density of combustion air islowered by mixing with the combustion gas (and steam) so that thecombustion reactivity of the air is restricted. The air having a lowoxygen density is mixed with the fuel gas of a low oxygen density whichhas been also diluted by the combustion gas, so that a combustionatmosphere at a low oxygen density is generated in the combustion area.As a result, a slow combustion reaction is caused in the combustion areaso that an extensive and even flame is created therein.

FIGS. 9(A), 9(B) and 10 are schematic cross-sectional views ofcombustion system with the fuel feeding device as shown in FIG. 2. InFIGS. 9 and 10, constituents, which are substantially the same as thoseof the aforementioned embodiments or equivalent thereto, are indicatedby the same reference numerals.

The combustion system as shown in FIGS. 9(A) and 9(B) is provided with ashunt passage R5 of a combustion gas introduction passage RG connectedto an air supply device 30. The combustion gas (and steam) through thepassage RG is divided at the conjunction of the passage R5 and a part ofthe combustion gas (and steam) is mixed with the combustion air in thedevice 30.

In the combustion apparatus as shown in FIG. 10, a shunt passage R5 ofan exhaust gas circulation passage R1 is connected to an air supplydevice 30A, and a shunt passage R6 of an exhaust gas circulation passageR2 is connected to an air supply device 30B. In a first combustion step(FIG. 10A), the combustion gas (and steam) of the passage R1 ispartially introduced into the device 30A through the passage R5 to bemixed with the combustion air. In a second combustion step (FIG. 10B),the combustion gas (and steam) of the passage R2 is partially introducedinto the device 30B through the passage R6 to be mixed with thecombustion air.

The other embodiments are shown in FIGS. 3(A), (B) and (C). In theseembodiments, an action of steam contained in the combustion gas isespecially emphasized, and a quantity of steam is mixed with a fuel, thesteam being heated to an extremely high temperature equal to or higherthan a temperature of 700 deg. C, preferably 1000 deg. C., morepreferably 1500 deg. C. That is, the aforementioned reforming reactionof hydrocarbon in the fuel is mainly considered to be effectivelyperformed in existence of high-temperature steam contained in thecombustion gas. In these embodiments, in order to develop such an actionof the high temperature steam, the sensible heat of the combustion gasis transmitted to steam so as to heat the steam up to an extremelyhigh-temperature equal to or higher than 700 deg. C., and thehigh-temperature steam is mixed with the fuel. The high-temperaturesteam acts as a reforming agent and a high-temperature heat medium, thefuel is reformed by such an action of high-temperature steam to be ahigh quality fuel containing a relatively large quantity of hydrocarbonradical, hydrogen, carbon, carbon monoxide and the like, and the fuel ismixed with the high-temperature combustion air to burn. In thecombustion apparatus as shown in FIGS. 3(A) and 3(B), the combustion gasis exhausted from the system after heating the steam.

FIGS. 11, 12 and 13 are schematic cross-sectional views of combustionapparatus with the fuel feeding device having the arrangement as shownin FIG. 3. The combustion system as shown in each of FIGS. 11, 12 and 13generally has an arrangement analogous to that shown in FIG. 6. However,a quantity of steam is supplied from a steam generator 8 to change-overmeans 20 and/or an air intake passage OA through a steam supply passageST. The steam is heated up to a high-temperature equal to or higher than700 deg. C. by heat-transfer contact with regenerators 14, 34, andthereafter, the steam is mixed with fuel. In FIG. 11, a first combustionstep (FIG. 11A) of the combustion system and a second combustion stepthereof (FIG. 11B) are illustrated, but only the first combustion stepof the combustion system is shown in FIGS. 12 and 13.

Another embodiment of the present invention is shown in FIG. 4. In aconcept that the high-temperature steam is mixed with the fuel topromote the reforming reaction of the fuel, the combustion systemillustrated in FIG. 4 is similar to that shown in FIG. 3. However, thefuel feeding device of this embodiment further comprises a steam heatingdevice for heating steam to a high-temperature. A fuel and combustionair for heating steam is fed to a combustion chamber of the steamheating device, and the steam of the steam generator is supplied to thecombustion chamber of the steam heating device. The steam gains thecombustion heat in the combustion chamber to be heated to ahigh-temperature equal to or higher than 700 deg. C. Thehigh-temperature steam is fed to a mixing area so as to be mixed with afuel to reform the fuel. The mixed gas of the fuel and steam as a highquality fuel gas is further mixed with high-temperature air to burn in acombustion area of the combustion system.

FIG. 14 is a schematic cross-sectional view of combustion system withthe fuel feeding device having the arrangement as shown in FIG. 4, andFIGS. 15 and 16 are cross-sectional views showing a structure of thesteam heating device.

As illustrated in FIG. 14, the steam heating device 80 is connected witha steam generator 8 through a steam supply passage LS, and connectedwith change-over means 20 through a high temperature steam supplypassage HS. The high-temperature steam is introduced into a mixing area15 of a fuel mixing device 10A in a first combustion step (FIG. 14A),and introduced into a mixing area 15 of a fuel mixing device 10B in asecond combustion step (FIG. 14B). In either step, the high-temperaturesteam is mixed with a fuel delivered from a fuel nozzle 11 andthereafter, flows into a combustion chamber 1 through a fuel gasinjection port 16. The high-temperature steam generates a hightemperature atmosphere in the mixing area 15 and takes a steam reformingreaction with the hydrocarbonaceous fuel to reform the fuel to a highquality fuel gas.

As illustrated in FIGS. 15 and 16, the steam generator 8 has a heatingfurnace body 88, a four-way valve 95 and switching control valves 85,86, 87. The body 88 is provided with a pair of honey-comb typeregenerators 81, combustion chambers 82, a combustion air delivery port83 and a fuel nozzle 84. Air and fuel of a combustion air supply passageSA and a fuel supply passage SF are alternately fed to either of thechambers 82 through the port 83 and the nozzle 84 under control of thevalves 85, 86, and steam of a steam supply passage LS is alternately fedto either of the regenerators 81 under control of the valve 95.High-temperature combustion gas produced in the chamber 82 is exhaustedthrough an exhaust passages EA, EG after heating the regenerator 81. Thesteam at a relatively low temperature is fed through a distributionpassage L1 or L2 to the regenerator 81 at a high temperature so as to beheated up to a temperature equal to or higher than 800 deg. C. byheat-transfer contact with the regenerator 81 and then, the steam flowsinto the supply passage HS to be fed to the change-over means 20 (FIG.14). If desired, the valve 87 is opened so that a part or all of thecombustion gas of an exhaust gas circulation passage R3 is introducedinto the passage LS through a combustion gas passage EB for mixing thecombustion gas in the steam flow of the passage LS.

With reference to FIGS. 17 to 26, preferred examples of the presentinvention is described hereinafter, in which constituents substantiallythe same as those shown in FIGS. 1 to 16 or equivalent thereto areindicated by the same reference numerals.

FIG. 17 is a cross-sectional view showing a combustion system with afuel feeding device of a first example according to the presentinvention. FIG. 17(A) shows a first combustion step of the combustionsystem and FIG. 17(B) shows a second combustion step thereof.

The system shown in FIG. 17 has a further embodied arrangement withrespect to the embodiment shown in FIG. 6, which includes air supplydevices 30A, 30B, passage change-over means 40 and an air supply fan 2,and which has fuel mixing devices 10A, 10B, passage change-over means 20and an exhaust gas circulation fan 3 constituting a fuel feedingapparatus. The change-over means 20, 40 is alternately switched to afirst position (FIG. 17A) and a second position (FIG. 17B). The fuelmixing devices 10A, 10B and the air supply devices 30A, 30B are fixed ona furnace body W of a combustion chamber 1 at a predetermined angle.Center axes of the devices 10A, 30A are oriented to intersect each otherin a combustion area of the chamber 1, and center axes of the devices10B, 30B are oriented to intersect each other therein.

The fuel mixing devices 10A, 10B are generally constructed by acylindrical casing 17, a regenerator 14 contained in the casing 17 and afuel nozzle 11 extending through the regenerator 14. A top portion ofthe casing 17 has a truncated-conic (frustoconical) reducing part 16 aand a fuel gas injection port 16 opens at a top face of the part 16 a. Afuel injection port 11 a of the nozzle 11 is located at a positionbackward from the port 16, so that a mixing area 15 is defined betweenthe ports 16 and 11 a. A bottom of the casing 17 is blocked by a bottomplate 19 and a combustion gas introduction part 12 is defined betweenthe regenerator 14 and the plate 19. The introduction part 12 is incommunication with a fuel gas port 18 which is connected with an exhaustgas circulation passage R1, R2. The fuel nozzle 11 extends through theplate 19 to be connected with a fuel supply pipe F1,F2, and fuel supplycontrol valves V1,V2 are provided on the pipes F1, F2 respectively.

Each of the air supply devices 30A, 30B is constructed by a cylindricalcasing 37 and a regenerator 34 contained in the casing 37. A top portionof the casing 37 has a truncated-conic (frustoconical) reducing part 36a and a combustion air delivery port 35 opens at a top face of the part36 a. A bottom of the casing 37 is blocked by a bottom plate 39 and acombustion air introduction part 32 is defined between the regenerator34 and the plate 39. The introduction part 32 is in communication with acombustion air port 38 which is connected with passages L1, L2.

The regenerator 14, 34 is a ceramic honey-comb structure of a latticeformation with a large number of cell apertures having a squarecross-section. The honey-comb structure has the cross-sectionaldimensions and length adapted for incorporation in the casing 17, 37 andeach of the cell apertures defines a narrow fluid passage for flow ofthe combustion gas or combustion air. The cell wall thickness and thepitch of the cell walls are preferably set to be the thickness and pitchwhich correspond to a maximum volumetric efficiency of the regeneratorand ensure the temperature effectiveness in a range of 0.7.1.0.

The passage change-over means 20 is defined by a high-speed switchingtype of four-way valve which can be selectively switched to a first orsecond position, and is provided with a plate-like valve body 26 securedon a rotational center shaft 25. The change-over means 20 has ports21,22 connected with the exhaust gas circulation passages R1, R2, andbypass ports 23,24 connected with exhaust gas circulation passages R3,R4. The passage R3 is connected with a suction port of the fan 3 and thepassage R4 is connected with a delivery port of the fan 3. An exhaustgas passage EG and a steam supply passage ST are connected to thepassage R4. If desired, a part of combustion gas is exhausted from thesystem and steam of a steam generator (not shown) is injected into thecombustion gas flow of the passage R4.

The change-over means 40 is a high speed switching type of four-wayvalve controllable to be switched to a first or second positionsimultaneously with the change-over means 20, and the means 40 isprovided with a plate-like valve body 46 fixed on a rotatable centershaft 45. The means 40 has an air supply port 41 connected with acombustion air supply passage CA, an exhaust gas port 42 connected withan exhaust gas passage E2, and ports 43, 44 connected with the passagesL1, L2 respectively.

In the first combustion step (FIG. 17A), the change-over means 20, 40 isheld in a first position. The combustion gas of the combustion chamber 1is sucked through the regenerator 14 of the device 10B by the fan 3. Thecombustion gas is pressed by the fan 3 and if desired, a quantity ofsteam of the passage ST is added to the combustion gas, and thereafter,the gas is delivered to the mixing area 15 through the regenerator 14 ofthe device 10A. The valve V1 feeds the fuel to the nozzle 11 of thedevice 10A, so that the fuel is delivered to the mixing area 15 of thedevice 10A. The fuel and combustion gas (and steam) are mixed with eachother, so that the mixed gas flows into the combustion chamber 1 throughthe port 16 as a fuel gas. The combustion gas in the chamber 1 is alsoextracted through the regenerator of the device 30B to the passage L2,and the gas is exhausted from the system through the change-over means40 and the passage E2 under exhaust gas induction pressure of an exhaustfan (not shown). The fan 2 introduces the combustion air into theregenerator 34 of the device 30A through the passages CA, L1 and thechange-over means 40. The combustion air through the regenerator 34flows into the combustion chamber 1 through the port 35. The fuel gasflow and the combustion air flow delivered from the devices 10A, 30A mixwith each other in the combustion chamber 1 and the fuel gas burns.

In the second combustion step (FIG. 17B), the change-over means 20, 40is held in a second position. The combustion gas of the combustionchamber 1 is sucked through the regenerator 14 of the device 10A by thefan 3. The combustion gas is pressed by the fan 3 and if desired, aquantity of steam of the passage ST is added to the combustion gas, andthereafter, the gas is delivered to the mixing area 15 through theregenerator 14 of the device 10B. The valve V2 feeds the fuel to thenozzle 11 of the device 10B, so that the fuel is delivered to the mixingarea 15 of the device 10B. The fuel and combustion gas (and steam) aremixed with each other, so that the mixed gas flows into the combustionchamber 1 through the port 16 as a fuel gas. The combustion gas in thechamber 1 is also extracted through the regenerator of the device 30A tothe passage L1, and the gas is exhausted from the system through thechange-over means 40 and the passage E2 under the pressure of theexhaust fan (not shown). The fan 2 introduces the combustion air intothe regenerator 34 of the device 30B through the passages CA, L2 and thechange-over means 40. The combustion air through the regenerator 34flows into the combustion chamber 1 through the port 35. The fuel gasflow and the combustion air flow delivered from the devices 10A, 30A mixwith each other in the combustion chamber 1 and the fuel gas burns.

The change-over means 20, 40 is alternately switched to either of firstand second positions in a predetermined time interval set to be nolonger than 60 seconds, so that the first step (FIG. 17A) and the secondstep (FIG. 17B) are alternately carried out. The regenerator 14 of eachof the fuel mixing devices 10A, 10B repeatedly takes either of a heataccumulating action for cooling the high-temperature combustion gas byheat-transfer contact therewith and a heat emission action for heatingthe cooled combustion gas up to an extremely high-temperature range byheat-transfer contact therewith. Therefore, the temperature of the gasthrough the passage R3, R4 is lowered to relieve the heat load andthermal stress of the fan 3 and the combustion gas (and steam) to bedelivered to the mixing area 15 is reheated to the temperature slightlylower than the temperature immediately after its extraction. Theregenerator 34 of each of the devices 30A, 30B repeatedly takes eitherof a heat accumulating action for cooling the high-temperaturecombustion gas by heat-transfer contact therewith and a heat emissionaction for heating the low-temperature combustion air up to an extremelyhigh-temperature range by heat-transfer contact with the air. Thus, thesensible heat of the combustion exhaust gas is transmitted to thecombustion air by means of the regenerator and the combustion air to bedelivered from the port 35 is continuously pre-heated to the extremelyhigh-temperature range.

As described above, the injection flows of high-temperature combustionair and mixed gas are injected from the ports 16, 35 to the combustionarea, so that the flows are mixed in an intersecting region of thecenter axes of the devices 10, 30 to form a high-temperature combustionatmosphere of a low oxygen density in the intersecting region. The port16,35 is restricted in its cross-sectional area of flow passage, and thevelocity of flow of the fuel gas and that of the combustion gas at theports 16,35 are set to be a high value, e.g., greater than 10 m/s, sothat high speed flows of the fuel gas and combustion air enters into thecombustion chamber 1. The fuel gas flow, which has a flow rateapproximately equivalent to the flow rate of the combustion air, has amomentum approximately equivalent to a momentum of the combustion air.This enables to carry out control of fuel gas flow, independently of thecombustion air flow.

That is, according to a conventional method of diluting a fuel with anin-furnace recirculation gas flow, a fuel is mixed with combustion gasby mixing a fuel injection flow with an in-furnace combustion gas flow,whereas, according to the present invention, the fuel injected from thefuel injection port 11 a is mixed with the high-temperature combustiongas (and steam) fed from an end of the regenerator 14 facing to thein-furnace area, so as to enter from the mixing area 15 into the furnaceas being the mixed gas flow (fuel gas injection flow) including a largequantity of high-temperature combustion gas (and steam). As the fuel hasbeen already mixed with the high-temperature combustion gas beforeentering the furnace, mixing thereof with an in-furnace combustion gasflow is unnecessary. Further, the fuel gas injection flow to beintroduced into the furnace has a momentum enough to be substantiallyindependent of the in-furnace combustion gas recirculation flow, so thatthe fuel gas effects an impingement mixing with the combustion air flowand slowly takes a combustion reaction. According to such a fuel feedingmethod, it is possible to optionally control the position and region formixing the fuel gas flow and the combustion air flow, independently ofthe in-furnace combustion gas recirculation flow.

Further, as the fuel and the combustion gas is mixed in the mixing area15, the mixing process and mixing ratio of the fuel and the combustiongas (and steam) can be optionally set, and control thereof can be surelycarried out. In addition, as the fuel gas flow has an enough momentum,the gas can be mixed with the combustion air flow at a desired positionin the furnace. Thus, the mixing process and mixing ratio of the fuel,combustion gas (and steam) and combustion air can be surely controlledin accordance with the aforesaid arrangement.

Furthermore, since the combustion gas has a relatively large quantity ofsteam injected thereto, and the gas is heated and then mixed with thefuel. Therefore, the fuel is reformed by a reforming action of thehigh-temperature steam contained in the combustion gas so as to be arelatively high or good quality fuel. The high-temperature combustiongas and steam also function as a high-temperature heat medium or heatsource for supplying to the mixing area 15 a quantity of sensible heatrequired for the steam reforming reaction of hydrocarbonaceous fuel(endothermic reaction).

Additionally, such a combustion method with use of a large quantity offuel gas flow entirely differs from the conventional combustion methodas described hereinbelow.

The high-temperature combustion gas (and steam) at a low oxygen densityfunctions as a high-temperature fuel carrier or means for increasing thefuel volume, which restricts a combustion reaction of the fuel andgreatly increase the momentum of the fuel. On the other hand, thehigh-temperature combustion air acts as an oxidizing agent causing aslow combustion reaction of the fuel gas by its self ignition in acombustion atmosphere of low oxygen density. Increased momentum of thefuel fluid diminishes affection of buoyancy involved in temperaturedifferences in the furnace, and prevents incomplete combustion and localheat resulting from its uneven and local mixing with the combustion air.As the fuel fluid with an independently controllable momentum is not soinfluenced by an in-furnace circulation flow of the combustion gas, theposition, condition and speed of mixing the fuel fluid with combustionair can be controlled by control of the fuel gas, whereby the positionand characteristics of flame can be desirably controlled.

Further, in the conventional high-cycle regenerative combustion system,the injected fuel flow from its delivery port is apt to shortly pass toa combustion exhaust gas port owing to an adjacent layout of the exhaustgas port and a delivery port of combustion air and fuel on a furnacewall, and vibration of in-furnace circulation flow and so forth is aptto be generated by a repeated switching operation of air supply andexhaust in a short time interval, so that vibration of injected fuelflow or vibration of mixed gas of fuel and air tends to be caused. Thiskind of fluid vibration may cause a thick and thin fuel condition,pulsating combustion and unstable combustion reaction in the combustionatmosphere, and therefore, an approach for surely avoiding suchconditions is desired. On the contrary, the combustion system of thearrangement as set forth above is capable of appropriately and surelymixing the fuel and combustion air in the combustion area and effectinga stable combustion therein, owing to increase of momentum of fuelfluid, whereby the aforementioned short pass of fuel, vibration of mixedgas and so forth can be prevented from occurring.

FIG. 18 is a cross-sectional view showing a combustion apparatus with afuel feeding device of a second example according to the presentinvention. FIG. 18(A) shows a first combustion step of the combustionapparatus and FIG. 18(B) shows a second combustion step thereof.

The apparatus shown in FIG. 18 is provided with passage change-overmeans 20, 40, an air supply fan 2 and an exhaust gas circulation fan 3which have substantially the same arrangements as those of the firstexample as set forth above. The change-over means 20, 40 is alternatelyswitched to a first position (FIG. 18A) and a second position (FIG. 18B)in a predetermined interval of time. In the present example, the fuelmixing device 10 has an integrally combined structure of the fuel mixingdevices 10A, 10B of the first example as described above, and the airsupply devices 30 has an integrally combined structure of the air supplydevices 30A, 30B of the first example.

The fuel mixing device 10 has a pair of regenerators 14A, 14B. In afirst combustion step (FIG. 18A), combustion gas of the combustionchamber 1 is extracted from the furnace through the second regenerator14B, and pressed by the exhaust gas circulation fan 3, and if desired, aquantity of steam is added to the combustion gas. The combustion gas(and steam) is delivered through the first regenerator 14A into a mixingarea 15 and mixed with a fuel injected from a fuel nozzle 11, and thegas flows into the chamber 1 as being a fuel gas. In a second combustionstep (FIG. 18B), the combustion gas of the combustion chamber 1 isextracted from the furnace through the regenerator 14A, and pressed bythe fan 3, and if desired, a quantity of steam is added to thecombustion gas. The combustion gas (and steam) is delivered through thesecond regenerator 14B into the mixing area 15 and mixed with the fuelinjected from the fuel nozzle 11, and the gas flows into the chamber 1as being the fuel gas. The change-over means 20 is controlled to bealternately switched to either of first and second positions, and theregenerator 14A, 14B repeatedly takes a heat accumulating action and aheat emission action. A fuel supply control valve V1 on a fuel supplypipe F1 normally feeds the fuel to the nozzle 11. The fuel is normallydelivered to the mixing area 15 and mixed with the high-temperaturecombustion gas (and steam) delivered from either of the regenerators14A, 14B, so that the mixed gas (fuel gas) is continuously produced.

Similarly, the air supply device 30 has a pair of regenerators 34A, 34Band a fuel nozzle 31 positioned between the regenerators 34A and 34B. Inthe first combustion step (FIG. 18A), the combustion gas of thecombustion chamber 1 is extracted from the furnace through the secondregenerator 34B, and exhausted through an exhaust passage E2. Thecombustion air is introduced into the combustion chamber 1 through thefirst regenerator 34A under the forced draft pressure of the fan 2. Inthe second combustion step (FIG. 18B), the combustion gas of thecombustion chamber 1 is extracted from the furnace through the firstregenerator 34A, and exhausted through an exhaust passage E2. Thecombustion air is introduced into the combustion chamber 1 through thesecond regenerator 34B under the forced draft pressure of the fan 2. Thechange-over means 40 is controlled to be alternately switched to eitherof first and second positions simultaneously with the change-over means20, and the regenerator 34A, 34B repeatedly takes a heat accumulatingaction and a heat emission action. The fuel nozzle 31 is connected witha fuel supply pipe F3 with a fuel supply control valve V3. The nozzle 31feeds a fuel only in a period (cold period) in which the furnacetemperature is relatively low, e.g., in a starting period of thecombustion system. A fuel injection port positioned at a front end ofthe nozzle 31 injects the fuel to cause in a combustion area, acombustion reaction with the combustion air containing a relativelylarge quantity of oxygen. The fuel nozzle 31 stops the fuel injection ina period (hot period) in which the furnace temperature rises up to apredetermined temperature.

The device 10, 30 is fixed on a furnace body W of the chamber 1 at apredetermined angle, and center axes of the devices 10, 30 are directedto intersect each other in the combustion area of the chamber 1. Thecombustion air flowing into the chamber 1 from the air supply device 30mixes with the mixed gas (fuel gas) flowing into the chamber 1 from thefuel mixing device 10 so as to take a combustion reaction.

According to such a combustion apparatus, controllability of mixingprocess and mixing ratio of fuel, combustion gas (and steam) andcombustion air is improved similarly to the aforementioned example, andalso, the fuel can be continuously injected from the fuel nozzle 11without switching control of fuel injection timing of the nozzle 11. Thefuel nozzle 31 may inject the fuel during the hot period, and in such acase, the fuel injection quantity may be reduced in the hot period.

FIG. 19 is a cross-sectional view showing a combustion system with afuel feeding device of a third example according to the presentinvention. FIG. 19 (A) shows a first combustion step of the combustionsystem and FIG. 19(B) shows a second combustion step thereof.

The apparatus shown in FIG. 19 is provided with passage change-overmeans 20, 40, an air supply fan 2 and an exhaust gas circulation fan 3which have substantially the same arrangements as those of the first andsecond examples as set forth above. The change-over means 20, 40 isalternately switched to a first position (FIG. 19A) and a secondposition (FIG. 19B) in a predetermined interval of time. Each of fuelinjection nozzles 11 is controlled synchronously with the change-overmeans 20, 40 to alternately inject a fuel.

In the present example, the fuel supply device comprises a fuel mixingdevice 10A incorporated in a combined combustion device 50A, and a fuelmixing device 10B incorporated in a combined combustion device 50B. Thisarrangement of the fuel supply device further embodies the embodiment asshown in FIG. 6.

The device 10A of the combined device 50A has a fuel nozzle 11, aregenerator 14, a casing 17 and a combustion gas introduction part 12.An air supply device 30A is provided with a regenerator 34 positionedoutside of the device 10A, a casing 37 and a combustion air introductionpart 32. A combustion gas port 18 is connected with an exhaust gascirculation passage R1, and a combustion air port 38 is connected with afluid passage L. Further, the nozzle 11 is connected with a fuel supplypipe F1 with a fuel supply control valve V1.

The combined device 50B is constituted from the devices 10B, 30B whichhave substantially the same arrangements as those of the devices 10A,30A, and the partial arrangements of the device 50B is symmetrical withthose of the device 50A. A combustion gas port 18 of the device 50B isconnected with an exhaust gas circulation passage R2, and a combustionair port 38 is connected with a fluid passage L2. Further, the nozzle 11of the device 10B is connected with a fuel supply pipe F2 with a fuelsupply control valve V2.

In a first combustion step (FIG. 19A), the combustion gas of thecombustion chamber 1 is extracted to the passages R2, L2 through theregenerator 14, 34 of the combined device 50B. The combustion gas of thepassage R2 is induced through the change-over means 20 by the exhaustgas circulation fan 3. The combustion gas is pressed by the fan 3 and ifdesired, a quantity of steam is injected into the combustion gas, andthereafter, the gas is delivered into a mixing area 15 through theregenerator 14 so as to be mixed with the fuel injected from the nozzle11, thereby flowing into the combustion chamber 1. On the other hand,the combustion gas of the passage L2 is exhausted from the systemthrough the change-over means 40 and an exhaust gas passage E2. Thecombustion air passes through the regenerator 34 of the combined device50A to flows into the combustion chamber 1 through a delivery port 35 ofthe combined device 50A.

In a second combustion step (FIG. 19B), the combustion gas of thecombustion chamber 1 is extracted to the passages R1, L1 through theregenerator 14, 34 of the combined device 50A. The combustion gas of thepassage R1 is induced through the change-over means 20 by the fan 3. Thecombustion gas is pressed by the fan 3 and if desired, a quantity ofsteam is injected into the combustion gas, and thereafter, the gas isdelivered into the mixing area 15 through the regenerator 14 of thedevice 50B so as to be mixed with the fuel injected from the nozzle 11,thereby flowing into the combustion chamber 1. On the other hand, thecombustion gas of the passage L1 is exhausted from the system throughthe change-over means 40 and the passage E2. The combustion air passesthrough the regenerator 34 of the combined device 50B to flows into thecombustion chamber 1 through the delivery port 35 of the combined device50B.

The change-over means 20, 40 is controlled to be synchronously switchedto either of first and second positions in a predetermined interval oftime set to be no longer than 60 seconds, and the regenerator 14, 34repeatedly takes a heat accumulating action and a heat emission action.The fuel gas flow and the combustion air flow delivered from the devices50A, 50B are mixed in the combustion area in the combustion chamber 1 totake a combustion reaction.

According to this example, the fuel fluid of the nozzle 11 is injectedinto a center part of the high-temperature combustion gas flow exitingfrom the regenerator 14, so that the fuel is mixed with the combustiongas from the center part of the combustion gas flow. The combustion airflows out from the regenerator 34 in such a manner that the air flowsurrounds the combustion gas flow, and reacts with the mixed gas (fuelgas) of the combustion gas and fuel from its peripheral zone. Therefore,the flow of combustion gas (and steam) forms an annular interferencezone for surely isolating the fuel injection flow and the combustion airflow, and the fuel fluid flow reacts with the combustion air after mixedwith the combustion gas (and steam), without the fuel directly reactingwith the combustion air.

FIG. 20 is a cross-sectional view showing a combustion system with afuel feeding device of a fourth example according to the presentinvention. FIG. 20 (A) shows a first combustion step of the combustionsystem and FIG. 20(B) shows a second combustion step thereof.

The example as shown in FIG. 20 is further embodies the embodiments asshown in FIGS. 1(C) and 8. A fuel nozzle 11 is positioned in acombustion gas introduction part 12 which functions as a mixing area 15.That is, in a first combustion step (FIG. 20A), the fuel injected by thenozzle 11 of a fuel mixing device 10A is mixed with a low-temperaturecombustion gas (and steam) in the mixing area 15 inside of the part 12,and the mixed gas passes through the regenerator 14 of the device 10A tobe heated by the regenerator 14 at a high-temperature. On the otherhand, in a second combustion step (FIG. 20B), the fuel injected by thenozzle 11 of a fuel mixing device 10B is mixed with the low-temperaturecombustion gas (and steam) in the mixing area 15 inside of the part 12,and the mixed gas passes through the regenerator 14 of the device 10B tobe heated by the regenerator 14 at a high-temperature. In this example,a fuel injection port 16 and a combustion air port 35 do not havereduced portions, but they have relatively large cross-sectional areas.The high-temperature mixed gas and combustion air injected from theports 16, 35 are mixed with each other in a combustion area of acombustion chamber 1 to take a combustion reaction. The otherarrangements and operations are substantially the same as those of thefirst example as shown in FIG. 17, and therefore, further detailedexplanations are omitted.

According to this example, the mixed gas gains the heat while passingthrough the regenerators 14 of the devices 10A, 10B to be heated up to ahigh-temperature, and thereafter, mixes with the high-temperaturecombustion air in the combustion area of the chamber 1 to generate anextensive flame in the combustion chamber 1 with the combustionatmosphere having a low oxygen density and a high-temperature.

FIG. 21 is a cross-sectional view showing a combustion system with afuel feeding device of a fifth example according to the presentinvention. FIG. 21 (A) shows a first combustion step of the combustionsystem and FIG. 21(B) shows a second combustion step thereof.

FIG. 21 shows an example which further embodies the embodiments as shownin FIGS. 2 and 10. Combustion air introduction parts 32 of air supplydevices 30A, 30B are in communication with shunt passages R5, R6 ofexhaust gas circulation passages R1, R2 by means of combustion gasintroduction port 60. Combustion gas (and steam) introduced into thepart 32 through the port 60 is mixed with combustion air, and the mixedfluid of air and combustion gas is pre-heated up to the aforementionedextremely high temperature range by the regenerator 34 and thereafter,flows into the furnace through a delivery port 35. According to such anarrangement, the combustion air, as well as the fuel, is mixed with thecombustion gas (and steam) before introduction into the furnace so thatthe combustion reactivity of the combustion air decreases. The mixed gasof combustion gas and air is introduced into the furnace, and itimpinges on and mixes with the flow of fuel gas in the in-furnacecombustion area, the fuel gas being similarly diluted by combustion gas(and steam), whereby a slow combustion reaction by a low oxygen densityis caused in the combustion area. The other arrangements and operationsare substantially the same as those of the example as shown in FIG. 17,and therefore, further detailed explanations are omitted.

FIG. 22 is a cross-sectional view showing a combustion apparatus with afuel feeding device of a sixth example according to the presentinvention. FIGS. 22(A) and 22(B) show first and second combustion stepsof the combustion apparatus, respectively.

FIG. 22 shows an example which further embodies the embodiments as shownin FIGS. 2 and 10. An exhaust gas passage EG is connected to a deliveryport of a circulation fan 3 and a steam supply passage ST1 of a steamgenerator 8 is connected to a bypass port 24 of a passage change-overmeans 20. The steam generator 8 is provided for an atmospheric airintake passage OA by means of a steam supply passage ST2. Steam of thegenerator 8 is supplied through the passages ST1:ST2 to the change-overmeans 20 and the passage OA, and brought into heat-transfer contact withregenerators 14, 34 to be heated up to a temperature equal to or higherthan 700 deg. C. The high-temperature steam delivered to a mixing area15 mixes with a hydrocabonaceous fuel of a fuel nozzle 11 so that thefuel is reformed to be a high quality fuel containing a relatively largequantity of hydrocarbon radical, hydrogen, carbon, carbon monoxide andso forth. According to such an arrangement, it is possible to reform arelatively heavy gravity or degraded quality hydrocabonaceous fuel suchas heavy oil to a light gravity or high quality fuel. The fuel gascontaining the reformed fuel is further mixed with a high-temperatureair and steam flowing out from a combustion air delivery port 35 intothe furnace, so that an extensive flame in a low oxygen density andhigh-temperature combustion atmosphere is created in the combustionchamber 1.

FIG. 23 is a schematic plan view showing a heating apparatus providedwith the combustion system according to the present invention. FIGS.23(A) shows a first combustion step of the combustion system and FIGS.23(B) shows a second combustion step thereof.

The heating apparatus is constituted to be a tubular furnace such as asteam reforming furnace. A number of heated tubes 5, through which afluid to be heated can pass, are arranged in a relatively overcrowdedcondition within a combustion chamber 1 of the heating apparatus. Thetube 5 constitutes a heated segment of the heating apparatus. Thecombustion apparatus is provided with fuel mixing devices 10A, 10B, airsupply devices 30A, 30B, change-over means 20, 40, an air supply fan 2and an exhaust gas circulation fan 3 which have substantially the sameconstructions as those of the combustion apparatus illustrated in FIG.16. The change-over means 20, 40 are alternately switched to either of afirst position (FIG. 23A) and a second position (FIG. 23B).

The heating apparatus is also provided with an auxiliary combustiondevice (not shown), and the combustion operation of the auxiliarycombustion device is carried out in a cold period in which a furnacetemperature is relatively low, e.g., in a starting period of the heatingapparatus. The auxiliary combustion device is rendered inoperative in ahot period in which the furnace temperature rises. The devices 10A, 10Bare operated in the hot period in which the furnace temperature has beenraised by operation of the auxiliary combustion device. In the firstcombustion step, combustion gas of the combustion chamber 1 is extractedfrom the furnace through regenerators 14, 34 of the devices 10B, 30B. Apredetermined flow rate of combustion gas is delivered to an exhaust gaspassage E2, and a predetermined flow rate of combustion gas passesthrough the regenerator 14 of the device 10A after addition of steam andflows into a mixing area 15 thereof, and then, it is mixed with a fueland introduced into the chamber 1 as the fuel gas. The device 30Aintroduces into the chamber 1, combustion air pre-heated up to theextremely high temperature range by the regenerator 34. In the secondcombustion step, combustion gas of the combustion chamber 1 is extractedfrom the furnace through regenerators 14, 34 of the devices 10A, 30A. Apredetermined flow rate of combustion gas is delivered to an exhaust gaspassage E2, and a predetermined flow rate of combustion gas passesthrough the regenerator 14 of the device 10B after addition of steam andflows into a mixing area 15 thereof, and then, it is mixed with a fueland introduced into the chamber 1 as the fuel gas. The device 30Bintroduces into the chamber 1, combustion air pre-heated up to theextremely high temperature range by the regenerator 34.

The devices 10A, 30A are directed toward a center area in the furnace inwhich the heated tubes 5 are arranged, and the fuel gas flow of a lowoxygen density at a high-temperature and a high velocity causes anintersecting impingement mixing and a combustion reaction with acombustion air flow at a high-temperature and a high velocity in acentral area of the furnace, in which the heated tubes 5 are denselyarranged. Such a heating method is intended to uniformly heat the wholecircumferential surface of the tube by a radiant heat-transmissioneffect and a convection heat-transmission effect of the flame itself.This essentially differs from the conventional heating method, i.e., theheating method in which both sides of the tube has to be heated, independence on the radiation heat transmission of gas and the solidradiation heat transmission of furnace wall, for uniformly heating thewhole circumferential surface of the tube.

In the present example, a large volume of thin fuel gas injected by thefuel mixing device 10 intersects and impinges with a high-temperaturecombustion air in the center area of the furnace so as to generate aslow combustion flame due to a high-temperature combustion atmosphere ata low oxygen density. The fuel gas containing a large volume ofcombustion gas causes a combustion atmosphere at a low oxygen density,which restricts the combustion reaction of the fuel components, and onthe other hand, the high-temperature combustion air urges self-ignitionof the fuel component and enables the combustion reaction of the fuelcomponent, even in the combustion atmosphere at a low oxygen density. Asa result, the fuel gas does not entirely burns immediately after mixingwith the combustion air, but the fuel component in the fuel gas causes aslow diffusion combustion in the high-temperature combustion atmosphereat the low oxygen density. Under such a combustion reaction, the flameis rendered stable and a local heat of flame is difficult to occur.

According to this heating method, it is possible to generate a flame inclose vicinity of the tube 5 without causing a local overheat of thetube 5, so that the entire circumference of the tube 5 can be heatedsubstantially uniformly. This differs from the conventional heatingmethod in which the flame is positioned away from the tube in order toprevent a local overheat of the tube.

Further, in accordance with the arrangement of the above heating device,the flows of fuel gas and combustion air at a high velocity are renderedin an intersecting impingement with each other in the center area of thefurnace in which the heated tubes 5 are densely arranged. Further, theflows induce the gas in the furnace to activate the convection thereof,and successive and irregular behavior of flame is normally caused invicinity of the tube 5. As a result, the relatively densely arrangedtubes 5 gain the heat uniformly in the entire circumference, owing tothe behavior of flame and activation of in-furnace gas convection, aswell as the increase of volume of flame and the uniformity of flametemperature which are caused in the low oxygen density and hightemperature combustion atmosphere. Further, as the first and secondcombustion steps are repeatedly switched in a short interval of time,the position and characteristics of flame are also varied in a shorttime by the switching control of the combustion steps. That is, thetemperature field and heating effect in the whole combustion area arealso equalized by such a switching motion of the combustion steps.

Such a control of the flame itself permits the equalization of theradiation and convection heat transfer effects, thereby enabling anincrease of density of the tubes 5. This allows the conventional type offurnace to be designed in a compacter size and enables new structuraldesigns of a heating furnace, which is advantageous in practice.

FIGS. 24 and 25 are schematic plan views showing alternative examples ofthe heating apparatus. An operation mode of the apparatus in a coldperiod is illustrated in FIG. 24 whereas an operation mode thereof in ahot period is illustrated in FIG.25. In the respective figures, (A)shows a first combustion step of the apparatus and (B) shows a secondcombustion step thereof.

The heating apparatus is constituted to be a tubular furnace such as asteam reforming furnace. A number of heated tubes 5 through which aheated fluid can pass, are arranged in a relatively overcrowdedcondition within a combustion chamber 1 of the heating apparatus. Thecombustion system shown in each of FIGS. 24 and 25 has an arrangementanalogous to that shown in FIG. 23. However, air heating devices 30A,30B are provided with fuel nozzles 31 for blowing a fuel in a coldperiod so as to take a combustion operation in the cold period. In theoperation mode during the cold period as shown in FIG. 24, the devices30A, 30B alternately perform, in a predetermined time interval, a firstcombustion step (FIG. 24A) in which the fuel and combustion air areblown from the device 30A and the combustion exhaust gas is exhaustedthrough the device 30B, and a second combustion step (FIG. 24B) in whichthe fuel and combustion air are blown from the device 30B and thecombustion exhaust gas is exhausted through the device 30A. Fuel mixingdevices 10A, 10B repeatedly carry out extraction and introduction of thecombustion gas in association with the devices 30A, 30B, but the devices10A, 10B do not delivery the fuel from nozzles 11, and therefore, thedevices 10A, 10B merely function as exhaust gas recirculation means.

On the other hand, in the operation mode during the hot period as shownin FIG. 25, the fuel nozzle 31 stops fuel injection and the air heatingdevice merely functions as combustion air introduction/extraction meansfor introducing the combustion air into the furnace and exhausting apart of in-furnace combustion gas from the furnace, and the fuel mixingdevices 10A, 10B carry out the first step (FIG. 25A) and the second step(FIG. 25B) alternately in a predetermined time interval. In the firststep, the mixed gas (fuel gas) of fuel, combustion gas and steam isblown through the device 10A and the combustion gas is extracted fromthe device 10B. In the second step, the mixed gas (fuel gas) of fuel,combustion gas and steam is blown through the device 10B and thecombustion gas is extracted from the device 10A. That is, thehigh-temperature combustion gas, which is produced in the furnace whenthe furnace temperature rises, is extracted from the furnace and then,mixed with steam and fuel, and thereafter, re-introduced into thefurnace as a high-temperature fuel gas to be mixed with the combustionair and burn in the combustion chamber 1.

In each of the combustion steps, the air heating device 10 and the fuelmixing device 10 introduce the combustion air and the fuel gas into thefurnace in directions crossing at a right angle. The combustion air andfuel gas are mixed mainly in a center area of the furnace by a mutuallyinducing action, and produce flame in vicinity of the tube 5 in acombustion atmosphere of a low oxygen density and a high-temperature.

FIG. 26 is a schematic cross-sectional view illustrating an example ofheating device wherein the arrangement of combustion system according tothe present invention is applied to a continuous firing type of heatingfurnace. FIG. 26(A) shows a first combustion step of the combustionsystem and FIG. 26(B) shows a second combustion step thereof.

The heating apparatus as shown in FIG. 26 constitutes a reductioncombustion zone in a steal heating furnace or a ceramic-industrial kilnwhich continuously heats or bakes works such as steel or ceramicmaterials in a reduction combustion atmosphere. Fuel mixing devices 10A,10B and air supply devices 30A, 30B are provided on a furnace body W ofa heating furnace, in which flame acts on works 6 successively moved ontransfer means 7. Similarly to the aforementioned example, first andsecond combustion steps are alternately carried out in a predeterminedtime interval. A fuel gas and high-temperature combustion air flowingout from the devices 10A, 10B, 30A, 30B generate flame in vicinity ofthe work 6.

The fuel gas delivered from the devices 10A, 10B into the furnace formsa lower flow moving along a surface of the work 6, and thehigh-temperature combustion air delivered from the devices 30A, 30Bforms an upper flow moving above the fuel gas flow. The flow of fuel gasat a low oxygen density generates a reduction combustion atmosphere invicinity of the upper surface of the work 6, and the flame produced bythe fuel gas and the high-temperature combustion air acts on the surfaceof work 6 as a reducing flame.

According to such an arrangement, a flattened flame can be caused forthe work 6 located at a center area of the furnace, and a reductioncombustion atmosphere surrounding the heated subject can be generated bythe fuel injection flow, whereby the heated subject can be heated in acondition to restrict oxidizing effect. For instance, in accordance withthe combustion system of the present example, a flattened fuel gas flowat a low oxygen density moving in vicinity of a material can begenerated in a metal heating furnace, ceramic-industrial kiln or thelike which carries out annealing or baking of material in a combustionatmosphere of reducing flame, whereby a reducing flame combustionatmosphere can be caused near the material.

Although preferred examples according to the present invention have beendescribed in detail, the present invention is not limited to suchexamples, but may be modified and changed without departing from thescope of the invention as claimed in the attached claims.

For instance, the above described examples employ a four-way valvestructure as the change-over means, but change-over means formed by acombination of valves may be employed.

Further, the arrangements of the fuel mixing device and the air heatingdevice are not limited to those described above, but a regenerativeheat-exchanger containing a number of regenerators can be employed asthe fuel mixing device and air heating device.

Furthermore, with respect to the aforementioned heating apparatus, thefuel mixing device and the air heating device may be positioned tooppose against each other, so that the fuel gas flow and the combustionair flow are introduced into the furnace as being a counterflow.

In addition, a process steam supply system in a factory or plant may beused as the steam supply means as set forth above.

INDUSTRIAL APPLICABILITY

As describe above, a fuel feeding apparatus and method according to thepresent invention can improve the controllability of mixing process andmixing ratio of fuel and combustion air.

Further, the fuel feeding apparatus and method according to the presentinvention allow the combustion gas and fuel to be optionally mixed,independently of control of in-furnace recirculation flow.

Furthermore, in accordance with the present invention, a fuel feedingapparatus and method are provided which can produce a fuel gas havingnew combustion characteristics.

From another aspect of the present invention, a combustion system andmethod are provided which can improve the controllability of fuel flowentering a combustion area and enable control of characteristics offlame by control of fuel flow, and further, a heating apparatus andmethod are provided which are capable of controlling properties of flameacting on heated subjects.

1. An apparatus for feeding fuel having a nozzle for feeding the fuel(F), a furnace for generating a combustion gas and/or steam supply meansfor supplying steam, said apparatus further comprising: a fuel mixingdevice for mixing fuel (F) from said nozzle with combustion gasextracted from said furnace and/or steam from said steam generator; acombustion area fluidly connected to said nozzle and said furnace and/orsteam generator, and means for mixing fuel gas with combustion airsupplied to said combustion area; fuel gas injection port forintroducing a mixed fluid from said fuel (F) with said combustion gasand/or steam into said combustion area as a fuel gas to mix the fuel gaswith combustion air supplied to said combustion area; wherein said fuelmixing device has a mixing area for mixing said fuel (F) with saidcombustion gas and/or steam and the fuel and the combustion gas and/orsteam are introduced into said mixing area for producing said fuel gasto be introduced into said combustion area; wherein the apparatusfurther comprises combustion gas cooling means for cooling saidcombustion gas and heating means for heating said combustion gas and/orsteam, wherein said mixing area is positioned between said cooling meansand said heating means; and wherein said cooling means and heating meansare provided with a regenerator which is in heat transfer contact withsaid combustion gas at a high temperature so as to effect heataccumulation, and which is in heat transfer contact with said mixedfluid so as to effect heat emission.
 2. A method for feeding fuelcomprising the steps of: feeding combustion gas extracted from a furnaceand/or steam of a steam generator to a mixing area; feeding said fuel(f) to said mixing area to produce a mixed fluid of the fuel with saidcombustion gas and/or steam; said mixed fluid is heated up to a hightemperature equal to or higher than 700° C. after the fuel (f) is mixedwith the combustion gas and/or steam; introducing said mixed fluid intoa combustion area as a fuel gas to mix the fuel gas with combustion airfed to the combustion area, thereby causing a combustion reaction ofsaid fuel gas in said combustion area; and wherein said mixed fluidintroduced into said combustion area is mixed with said combustion airpre-heated up to a temperature equal to or higher than 700° C.
 3. Adevice for producing a fuel gas which includes a fuel feeding devicecomprising: a plurality of mixing devices each having a mixing area formixing a fuel of said fuel feeding device with steam of a steamgenerator; a passage change-over device for switching a fluid passage ofsaid steam leading to said mixing device; a regenerator having ahoney-comb structure for heating said fuel and said steam after the fuelis mixed with the steam; wherein the fuel and the steam are introducedinto said mixing area (15) to produce a mixed fluid of the fuel withsaid steam; wherein the regenerator is in heat transfer contact withsaid mixed fluid passing therethrough, so that the mixed fluid is heatedup to a high temperature equal to or higher than 700 deg. C.; andwherein said fuel feeding device is provided with a fuel control valvefor switching a fuel supply passage in synchronism with said change-overdevice.